1. Field of the Invention
The present invention relates to a semiconductor device containing a circuit structured by a thin film transistor (hereinafter referred to as a TFT), and to a method of manufacturing thereof. For example, the present invention relates to an electro-optical device, typically a liquid crystal display panel, and to electronic equipment (electronic instruments) loaded with this type of electro-optical device as a part.
Note that, throughout this specification, the term semiconductor device indicates general devices which function by utilizing semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic equipment are all semiconductor devices.
2. Description of the Related Art
Techniques of structuring a thin film transistor (TFT) using a semiconductor thin film (having a thickness on the order of several nm to several hundreds of nm) formed on a substrate having an insulating surface have been in the spotlight in recent years. The thin film transistor is widely applied in electronic devices such as ICs and electro-optical devices, and in particular, its development is accelerating as a switching element of a liquid crystal display device.
Active matrix liquid crystal display devices which use TFTs as switching elements for connecting to pixel electrodes arranged in a matrix shape are gathering attention for use in obtaining a high quality image in a liquid crystal display device.
Active matrix liquid crystal display devices are roughly divided into two types, a transmitting type and a reflecting type.
In particular, the reflecting type liquid crystal display device has the advantage of low energy consumption compared to the transmitting type liquid crystal display device because it does not use a backlight, and its demand in direct view displays for mobile computers and video cameras is high.
Note that the reflecting type liquid crystal display device utilizes the optical modulation action of a liquid crystal, and a state of outputting incident light, which is reflected by pixel electrodes, to the outside of the device, and a state of not outputting incident light to the outside of the device are selected, performing bright and dark display. In addition, display of an image is performed by combining these two states. The pixel electrodes in a reflecting type liquid crystal display device are generally composed of a metallic material having a high light reflectivity, such as aluminum, and these are electrically connected to switching elements such as thin film transistors.
Gate wirings (scanning lines), source wirings (signal lines), and capacitor wirings are each patterned into a linear shape with the pixel structure of a conventional reflecting type liquid crystal display device. Further, the source wirings are arranged in a horizontal direction, the gate wirings are arranged in a vertical direction, and interlayer insulating films are formed between the gate wirings and the source wirings in order to insulate the wirings. In addition, in a conventional structure, a portion of the source wirings and a portion of the gate wirings intersect, and TFTs are arranged in the vicinity of the intersecting portions.
Furthermore, an additional interlayer insulating film is formed on the source wirings conventionally, and the pixel electrodes are formed on this interlayer insulating film. The number of steps increases when the number of layers increases with this structure, and this invites an increase in costs.
A structure in which pixel electrodes are formed between source wirings at the same time the source wirings are formed is known as another conventional structure. In this case, it is necessary to perform shielding by using a black matrix between the source wirings and the pixel electrodes.
Shielding of a TFT and shielding between pixels are conventionally performed in accordance with a black matrix, in which a metallic film formed of a material such as chrome is patterned into a desired shape. However, in order to have sufficient shielding of light by the black matrix, it is necessary to insulate by forming an interlayer insulating film between the black matrix and the pixel electrodes. If the number of layers of interlayer insulating films thus increases, the number of steps increases, inviting increased costs. Further, it is disadvantageous to have interlayer insulating properties. In addition, the number of steps for forming the black matrix itself and the number of masks are increased.
Seen from the viewpoint of display performance, a storage capacitor and a high aperture ratio are required for pixels. By giving each pixel a high aperture ratio, the efficiency of light usage increases, and the display device can be made energy efficient and small in size.
The reduction in the size of pixels has been advancing in recent years, and higher definition images are demanded. The reduction in pixel size means that the amount of surface area occupied for forming a TFT and wirings for each pixel becomes larger, and the aperture ratio of the pixels decreases.
In order to obtain a high aperture ratio in each pixel within standard size pixels, it is indispensable to layout the circuit elements required in the circuit structure of the pixel very efficiently.
A completely new pixel structure, not found conventionally, is thus required in order to realize a reflecting type liquid crystal display device having a high pixel aperture ratio by using a small number of masks.
In order to respond to the above demands, an object of the present invention is to provide a reflecting type liquid crystal display device having a pixel structure in which a high aperture ratio is achieved without increasing the number of masks and the number of steps.
In order to solve the problems associated with conventional techniques, the following means are devised.
The present invention has a pixel structure in which TFTs and pixels are shielded without using a black matrix. In order to shield between pixels, gate wirings and source wirings are formed on the same insulating film (first insulating film), and pixel electrodes are arranged overlapping the gate wirings or the source wirings, sandwiching an insulating film (second insulating film) therebetween. Further, in order to shield the TFTs from light, color filters (a red color filter, or a lamination film of a red color filter and a blue color filter) are arranged on an opposing substrate as light shielding films overlapping the TFTs on an element substrate.
According to the structure of the present invention disclosed in this specification, as shown in an example of FIG. 1, there is provided a semiconductor device comprising:
a first semiconductor layer and a second semiconductor layer on an insulating surface;
a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a gate wiring on the first insulating film, overlapping the first semiconductor layer;
a capacitor wiring on the first insulating film, positioned over the second semiconductor layer;
an island shape source wiring on the first insulating film;
a second insulating film covering the gate wiring, the capacitor wiring, and the island shape source wiring;
a connection electrode on the second insulating film, connected to the island shape source wiring and the first semiconductor layer; and
a pixel electrode on the second insulating film, connected to the first semiconductor layer;
characterized in that the pixel electrode overlaps the island shape source wiring, sandwiching the second insulating film therebetween.
According to the above structure, a plurality of the island shape source wirings are arranged in each pixel, and the island shape source wirings are each connected to the connection electrodes. Further, the pixel electrode overlaps the gate wiring, sandwiching the second insulating film therebetween.
According to another structure of the present invention, a semiconductor device comprising a first substrate, a second substrate, and a liquid crystal maintained between the joined first substrate and second substrate, characterized in that:
a pixel portion having a thin film transistor, and a driver circuit, having a thin film transistor are formed on the first substrate;
the pixel portion has a semiconductor layer, a first insulating film covering the semiconductor layer, wirings on the first insulating film, a second insulating film covering the wirings, and electrodes on the second insulating film;
a red color filter, a blue color filter, and a green color filter corresponding to each pixel of the pixel portion are formed on the second substrate; and
a lamination film of the red color filter and the blue color filter on the second substrate becomes a light shielding film overlapping the thin film transistor on the first substrate.
According to the above structure, the wirings are a gate wiring, an island shape source wiring, and a capacitor wiring. The storage capacitor having the first insulating film as a dielectric is formed in a region in which the capacitor wiring and the semiconductor layer overlap, sandwiching the first insulating film therebetween. The electrodes are a pixel electrode connected to the semiconductor layer, and a connection electrode connected to the island shape source wiring.
According to the above structure, a gap between the first substrate and the second substrate is maintained by a spacer composed of a lamination film of the red color filter, the blue color filter, and the green color filter.
According to another structure of present invention, as shown in an example of FIG. 10, there is provided a semiconductor device comprising:
a first semiconductor layer and a second semiconductor layer on an insulating surface;
a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a first electrode on the first insulating film, overlapping the first semiconductor layer;
a second electrode on the first insulating film, overlapping the second semiconductor layer;
a source wiring on the first insulating film;
a second insulating film covering the first electrode and the source wiring;
a gate wiring on the second insulating film, connected to the first electrode;
a connection electrode on the second insulating film, connected to the source wiring and the first semiconductor layer; and
a pixel electrode on the second insulating film, connected to the first semiconductor layer;
characterized in that the pixel electrode overlays the source wiring, sandwiching the second insulating film therebetween.
According to the above structure, the first electrode overlapping the first semiconductor layer is a gate electrode. The storage capacitor is formed by the second semiconductor layer connected to the pixel electrode, and the second electrode connected to a gate wiring of an adjacent pixel, with the first insulating film as a dielectric.
According to the above structure, the gate wiring is formed of a film having an element selected from the group consisting of: polysilicon doped with an impurity element which imparts one conductivity; W; SIX; Al; Cu; Ta; Cr; and Mo as its main constituent, or a lamination film of the elements.
According to the above structure, the second insulating film is composed of a first insulating layer having silicon as its main constituent, and a second insulating layer formed of an organic resin material.
Further, according to another structure of the present invention, there is provided a semiconductor device comprising TFT containing a semiconductor layer formed on an insulating surface, an insulating film formed on the semiconductor layer, and a gate electrode formed on the insulating film, characterized in that:
the gate electrode has a first conductive layer with a tapered shape edge portion as a lower layer, and a second conductive layer having a narrower width than that of the first conductive layer as an upper layer; and
the semiconductor layer includes: a channel forming region overlapping the second conductive layer, sandwiching the insulating film therebetween; a third impurity region formed contacting the channel forming region; a second impurity region formed contacting the third impurity region; and a first impurity region formed contacting the second impurity region.
Further, an angle formed between the inclined surface of the first conductive layer and the horizontal plane (also referred to as a taper angle) is smaller than an angle formed between the inclined surface of the second conductive layer and the horizontal plane. For convenience, the inclined surface having the taper angle is referred to as a tapered shape, and a portion having the tapered shape is referred to as a tapered portion, throughout this specification.
Furthermore, according to the above structure, the third impurity region overlaps the first conductive layer, sandwiching the insulating film therebetween. The third impurity region is formed by doping an impurity element into the semiconductor layer, through the first conductive layer having the tapered portion in the edge portion, and through the insulating film. Further, the depth to which an ion is injected during doping is shallower the thicker the material layer arranged on the semiconductor layer becomes. The concentration of the impurity element added within the semiconductor layer therefore also changes by being influenced by the film thickness of the conductive layer having the tapered shape. The concentration of the impurity element within the semiconductor layer decreases in accordance with an increase in film thickness of the first conductive layer, and the concentration increases as the film thickness becomes thinner.
According to the above structure, the first impurity region is a source region or a drain region.
Further, according to the above structure, a region of the insulating film which overlaps with the second impurity region contains a tapered portion. The second impurity region is formed by doping an impurity element into the semiconductor layer through the insulating film. The impurity concentration distribution of the second impurity region therefore also changes, being influenced by the tapered portion of the insulating film. The impurity concentration within the second impurity region decreases in accordance with an increase in film thickness of the insulating film, and the concentration increases as the insulating film thickness decreases. Note that, although the second impurity region is formed by the same doping as the third impurity region, the second impurity region does not overlap with the first conductive layer. Therefore, the impurity concentration of the second impurity region is higher than the impurity concentration of the third impurity region. Further, the width of the second impurity region in the channel longitudinal direction is the same width as the third impurity region, or is wider than the width of the third impurity region.
According to the above structure, the TFTs are n-channel TFTs or p-channel TFTs. Further, pixel TFTs are formed, using n-channel TFTs in the present invention, and driver circuits are provided with CMOS circuits using n-channel TFTs or p-channel TFTs.
Further, according to the above structure, the semiconductor device is a reflecting type liquid crystal display device.
According to a structure of the present invention in manufacturing process for attaining the above constitution, there is provided a method of manufacturing a semiconductor device, comprising:
a first step for forming a first semiconductor layer and a second semiconductor layer, made of crystalline semiconductor films, on an insulating surface;
a second step for forming a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a third step for forming: a gate wiring on the first insulating film, overlapping the first semiconductor layer; a capacitor wiring on the first insulating film, positioned over the second semiconductor layer; and an island shape source wiring on the first insulating film;
a fourth step for forming a second insulating film covering the gate wiring, the capacitor wiring, and the island shape source wiring; and
a fifth step for forming: a connection electrode on the second insulating film, connected to the island shape source wiring and to the first semiconductor layer; and a pixel electrode overlapping the island shape source wiring.
According to another structure of the present invention in the manufacturing process for attaining the above constitution, there is provided a method of manufacturing a semiconductor device having a liquid crystal sandwiched between a pair of substrates, comprising:
a first step for forming a first semiconductor layer, and a second semiconductor layer, made of crystalline semiconductor films, on a first substrate:
a second step for forming a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a third step for forming: a gate wiring on the first insulating film, overlapping the first semiconductor layer; a capacitor wiring on the first insulating film, positioned over the second semiconductor layer; and an island shape source wiring on the first insulating film:
a fourth step for forming a second insulating film covering the gate wiring, the capacitor wiring, and the island shape source wiring;
a fifth step for forming: a connection electrode on the second insulating film, connected to the island shape source wiring and to the first semiconductor layer; and a pixel electrode overlapping the island shape source wiring;
a sixth step for forming, on the second substrate, a red color filter, a blue color filter, and a green color filter corresponding to each pixel electrode, and for simultaneously forming a light shielding film, composed of a lamination film of the red color filter and the blue color filter, so as to overlap with at least the first semiconductor layer; and
a seventh step for joining the first substrate and the second substrate.
According to another structure of the present invention in the manufacturing process for attaining the above constitution, there is provided a method of manufacturing a semiconductor device, comprising:
a first step for forming a first semiconductor layer and a second semiconductor layer, made of crystalline semiconductor films, on an insulating surface;
a second step for forming a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a third step for forming, on the first insulating film: a first electrode overlapping the first semiconductor layer; a second electrode overlapping the second semiconductor layer; and a source wiring;
a fourth step for forming a second insulating film covering the first electrode, the second electrode, and the source wiring; and
a fifth step for forming, on the second insulating film: a gate wiring connected to the first electrode; a connection electrode connected to the first semiconductor layer and to the source wiring; and a pixel electrode overlapping the source wiring.
According to the above structure, the second semiconductor layer connected to the pixel electrode overlaps the second electrode connected to a gate wiring of an adjacent pixel, sandwiching the first insulating film therebetween.
Further, according to another structure of the present invention in the manufacturing process for attaining the above constitution, there is provided a method of manufacturing a semiconductor device having a liquid crystal sandwiched between a pair of substrates, comprising:
a first step for forming a first semiconductor layer, and a second semiconductor layer, made of crystalline semiconductor films, on a first substrate;
a second step for forming a first insulating film on the first semiconductor layer and on the second semiconductor layer;
a third step for forming, on the first insulating film: a first electrode overlapping the first semiconductor layer; a second electrode overlapping the second semiconductor layer; and a source wiring;
a fourth step for forming a second insulating film covering the first electrode, the second electrode, and the source wiring;
a fifth step for forming, on the second insulating film: a gate wiring connected to the first electrode; a connection electrode connected to the first semiconductor layer and to the source wiring; and a pixel electrode overlapping the source wiring;
a sixth step for forming, on the second substrate, a red color filter, a blue color filter, and a green color filter corresponding to each pixel electrode, and for simultaneously forming a light shielding film, composed of a lamination film of the red color filter and the blue color filter, so as to overlap with at least the first semiconductor layer; and
a seventh step for joining the first substrate and the second substrate.
According to another structure of the present invention in the manufacturing process for attaining the above constitution, there is provided a method of manufacturing a semiconductor device, comprising the steps of:
forming a semiconductor layer on an insulating surface;
forming an insulating film on the semiconductor layer;
forming a first conductive layer and a second conductive layer on the insulating film;
adding an impurity element which imparts one conductivity, using the first conductive layer and the second conductive layer as a masks forming a first impurity region;
etching the first conductive layer and the second conductive layer, forming a first conductive layer having a tapered portion and a second conductive layer having a tapered portion; and
adding an impurity element which imparts one conductivity into the semiconductor layer through the insulating film, forming a second impurity region, and simultaneously adding an impurity element which imparts one conductivity into the semiconductor layer, through the tapered portion of the first conductive layer, forming a third impurity region in which the impurity concentration increases toward an edge portion of the semiconductor layer.
Furthermore, according to another structure of the present invention in the manufacturing process for attaining the above constitution, there is provided A method of manufacturing a semiconductor device, comprising the steps of:
forming a semiconductor layer on an insulating surface;
forming an insulating film on the semiconductor layer;
forming a first conductive layer and a second conductive layer on the insulating film;
adding an impurity element which imparts one conductivity, using the first conductive layer and the second conductive layer as a mask, forming a first impurity region;
etching the first conductive layer, the second conductive layer, and the insulating film, forming a first conductive layer having a tapered portion and a second conductive layer having a tapered portion, and an insulating film having a portion of the tapered portion; and
adding an impurity element which imparts one conductivity into the semiconductor layer, through the insulating film having a portion of the tapered portion, forming a second impurity region; and simultaneously adding an impurity element which imparts one conductivity into the semiconductor layer, through the tapered portion of the first conductive layer, forming a third impurity region in which the impurity concentration increases toward an edge portion of the semiconductor layer.